Recently, lighting devices have been developed that make use of light emitting diodes (LEDs) for a variety of lighting applications. Owing to their long lifetime and high energy efficiency, LED lamps are now also designed for replacing traditional incandescent and fluorescent lamps, i.e., for retrofit applications. For such applications, the LED retrofit lamp is typically adapted to fit into the socket of the respective lamp fixture to be retrofitted. Moreover, since the maintenance of a lamp is typically conducted by a user, the LED retrofit lamp should ideally be readily operational with any type of suitable fixture without the need for re-wiring the fixture. In particular, it is desirable to also reuse the ballasts that are already in place in the fixtures in order to ease the installation procedure.
LEDs typically exhibit a higher luminous efficacy than common light sources and thus draw less current from a power supply for a given luminuous flux. While this fact is advantageous for the present efforts of energy conservation, difficulties may arise when retrofitting a lamp fixture that is designed for a nominal power. For this reason, an LC circuit is typically added to the LED retrofit lamp in order to adapt the current and the voltage provided by the ballast to the LED retrofit lamp. However, some high frequency electronic ballasts that comprise a (passive) power factor correction (PFC) unit may have notably different output characteristics when they are connected to the LC circuit comprised by LED retrofit lamp. For instance, it may be that the current provided by the high frequency electronic ballast is considerably increased. This means that also the current flowing through the resonant inductor of the LC resonant circuit comprised by the high frequency electronic ballast, which is related to the provided current, may be increased up to a level at which it could overstress the resonant inductor. Such an overcurrent situation may result in safety problems for the high frequency electronic ballast, e.g. it may result in an overheating of the high frequency electronic ballast.